In the building industry, and particularly the art of prefabricated concrete building structures, it has been known for some time that in order to avoid the cost of transporting rather large and heavy precast concrete panels from a central point at which they are manufactured in a casting plant to the site of the concrete building structure, that the panels could be cast at the site. The method developed involves forming conventional wooden forms in the shape of generally rectangular frames corresponding to the shape of the concrete panel and laying one of these frames on a flat base and casting the panel within the wooden form. In order to conserve space, the method has been developed of covering the lowermost such cast panel with a parting material, such as a sheet of plastic, and casting a second panel on top of the first panel, and proceeding to cast a series of panels in a stack. After the panels have cured, they can be unstacked and the wooden forms removed, and the panels can be incorporated into the building structure.
However, as the art of prefabricated concrete building structures has improved, methods have been developed for directly joining the edges of the panels to each other and filling the joints with a grouting material for sealing the joints, to facilitate the erection of the building. Such panels must have specially shaped edge portions in order to make it possible to joint the panels together directly into the finished concrete building structure. The method of precasting the panels at the site of the building structure has been difficult to adapt to the casting of such specially shaped panels.
In U.S. Pat. No. 2,940,295, there is disclosed pre-cast edge frames of concrete which are pre-cast, and then the frame members are arranged in a frame, the exterior peripheral edge of which has a plain flat shape. Then the center portion of the panel is cast into the thus formed frame, which frame serves as the form for the concrete for the center portion of the panel and also becomes the peripheral edge of the finished panel. It is conceivable that the outer peripheral edges of the frame in this patent could be given the desired shape when they are initially cast, and then these frame members could be transported to the construction site and used as the forms for the panels in place of the wooden forms. The edges of the finished panels could thus be given the desired shapes.
While this would be an improvement over the prior art methods, such a system would still require a central casting plant and still necessitate the transport of the pre-cast concrete frame members to the site of the building structure. Where the site of the building structure is relatively close to the casting plant, this might not involve any great expense or difficulty. However, where the concrete structure is to be erected at a site remote from the central casting plant, the transport of the pre-cast concrete frame members might create considerable difficulty, and involve considerable expense.
Moreover, such a system would involve the formation of a joint between the pre-cast concrete frame members and the central portion of the panel. Care would have to be taken during the casting of the panels at the building site to insure that this joint was properly formed so as not to leave an aperture of any kind or a weak portion of the finished panel.